The present disclosure relates generally to systems, methods, and devices for facilitating access to a target anatomical site. More specifically, the present invention provides methods and structures for detecting or facilitating positioning of a probe (e.g. a needle) in the spinal canal of a patient.
A number of medical procedures involve gaining probe access to a patient's spinal canal. Accurately or reliably determining entry or positioning of a medical instrument in the spinal canal is often crucial for optimal delivery of care.
For instance, delivery of epidural anesthesia, a type of anesthesia commonly used in childbirth, involves the insertion of a catheter into the epidural space. To introduce the catheter, a special epidural needle is advanced through the back and into the epidural space; the catheter is then inserted through the needle and into the epidural space. During its passage into the body, the needle passes through skin and soft tissue before entering a tough ligament. The epidural space is just beyond the ligament. The needle must be advanced far enough to reach the epidural space, while advancing too distally should be avoided. If the needle is put in too far, it will pass through the epidural space and puncture a thin layer of tissue (the dura), entering the subarachnoid space and causing a cerebrospinal fluid (CSF) leak.
Accurate positioning of a probe or catheter in the epidural space is a process requiring a degree of precision. Most doctors identify the epidural space using a “loss of resistance” technique, in which the epidural needle is attached to a “loss of resistance” syringe having a plunger that moves back and forth with very little resistance. The needle and syringe are slowly advanced into the patient's back while the plunger is occasionally depressed to test for a “loss-of-resistance.” If the needle is in the tough ligament located between the skin and the epidural space, the plunger will not depress easily. If the needle is in the epidural space, however, the plunger will depress more easily. Once the needle is in the epidural space, an epidural catheter is inserted through the needle and into the epidural space. The catheter is then used to deliver anesthesia or other drugs. Sometimes the drug is injected directly into the epidural space through a needle and a catheter is not inserted.
Unfortunately, complications due to faulty positioning or placement of the probe or catheter are not uncommon during epidural procedures. One of the most frequent complications occurs when the epidural needle is accidentally inserted past the epidural space and through the dura, resulting in a cerebrospinal fluid (CSF) leak. Following accidental dural puncture, patients have a greater than 50% chance of developing a post-dural puncture headache (PDPH) resulting from CSF loss. These headaches are often severe and associated with nausea and vomiting, vision and hearing changes, low back pain, dizziness, and cranial nerve palsies. Most of these headaches go away in about a week, but in some instances can last for months or years. Additionally, if left untreated, the headaches can predispose to subdural hematoma and possibly death.
Another common error during epidural anesthesia occurs when a catheter is introduced in an area other than the epidural space, like the surrounding muscles. This error happens because, due to tissue structure differences, these areas can give a false “loss of resistance” upon epidural needle entry. Unfortunately, it is difficult and time consuming to identify misplaced catheters. The current most reliable practice for verifying that a catheter is correctly placed in the epidural space is an injection of local anesthetic and subsequent verification of drug effect. The drug will not take effect if the catheter is not in the epidural space, and since peak effect of correctly delivered drug can take up to 20 minutes, verification by this method can be time consuming. Such a delay can be impractical for a patient in severe pain, and may in fact be dangerous for a woman in need of an urgent caesarean section. In addition to prolonging pain relief, such misplacement necessitates additional procedures, such as additional attempt at epidural anesthesia or even emergency general anesthesia.
Both problems, puncturing the dura and putting the catheter in the wrong place, result because the “loss-of-resistance” technique is simply not particularly sensitive. Further, there is a lack of a suitable alternative that does not involve impractical complexity.
Lumbar puncture is another medical procedure requiring access to the spinal cavity. During a lumbar puncture (or spinal tap) a needle is inserted through a patient's back and into the subarachnoid space to measure the intracranial pressure (“opening pressure”) and to collect a sample of cerebrospinal fluid (CSF) for lab analysis. A lumbar puncture is the most reliable method to diagnose meningitis, a life-threatening but highly treatable infection characterized by high fevers, headache, a stiff neck, and elevated CSF pressure. Infants commonly require lumbar puncture as a part of the routine workup for fever without a source, as they have a much higher risk of meningitis than adults and do not reliably show external signs of meningitis, like a stiff neck. Lumbar punctures are also performed to diagnose subarachnoid hemorrhage, hydrocephalus, and idiopathic intracranial hypertension, and to inject medications into the cerebrospinal fluid, particularly spinal anesthetics and chemotherapeutics.
Like epidural procedures, gaining access to the spinal cavity for a lumbar puncture typically relies on the physician's senses of touch or feel. To perform a lumbar puncture, the physician slowly advances a needle into the back until he feels a tactile “pop”, stopping needle advancement occasionally to look for return of CSF through the end of the needle in case the pop isn't noticed. The “pop” signals the passage of the needle through a tough membrane called the dura and into the subarachnoid (CSF) space. Unfortunately, the “pop” is not as noticeable in some adult patients as well as in infants generally. Additionally, often the only way to tell when the needle is in the right place is by looking for the return of CSF through the back of the needle. The CSF may take tens of seconds to make its way out the end of the needle, and the physician may have to reposition the needle multiple times before seeing CSF return through the needle, making the procedure very time consuming and uncomfortable for the patient. If the physician advances the spinal needle too far, the needle can damage the blood vessels at the distal side of the CSF space and cause what is known as a “bloody tap” that contaminates the CSF sample and frequently leads to additional procedures. Unfortunately, nearly 20% of pediatric lumbar punctures result in a “bloody tap”, in part because the physicians do not have a good indication of when the needle has entered the correct space.
Once the needle is in the CSF space, the physician can measure the CSF opening pressure. Measurement of CSF pressure has long been recommended as part of the lumbar puncture procedure, and is typically accomplished using a liquid column hydrostatic manometer. A liquid column hydrostatic manometer only allows pressure measurement once CSF is obtained, because the height of the column of CSF flowing out of the needle and filling the manometer tube is used to determine the pressure. The manometer is connected to the end of the LP needle directly or via a three-way stopcock. An assistant is typically required to hold the top end of the tube. It can be difficult to perform this measurement for a number of reasons, including the following: potential for attachment and removal of the apparatus and patient movement to dislodge the needle; relatively long time (e.g., several minutes) to acquire a reading; potential for inaccuracy from air bubbles; loss of CSF increasing post-dural puncture headache frequency. Because of these problems, CSF pressure is often not measured during lumbar puncture in children.
Accordingly, improved methods and structures are needed for facilitation of probe access and/or positioning in a spinal canal of a patient, and could significantly improve efficiency and reduce complications associated with many medical procedures such as lumbar punctures and epidural access procedures.